An ultrasonic diagnostic apparatus irradiates ultrasonic waves to the inside of a subject, especially a living body, such as a person or an animal to detect an echo signal reflected from the inside of the living body and then displays tomographic images of tissues inside the living body, thereby providing information necessary for diagnosis of the subject. In such a case, the ultrasonic diagnostic apparatus uses an ultrasonic probe in order to transmit the ultrasonic waves to the inside of the subject and receive the echo signal from the inside of the subject.
FIG. 12 illustrates an example of such an ultrasonic probe. In FIG. 12, an ultrasonic probe 20 is configured to include a plurality of piezoelectric elements 11 arranged in a predetermined direction so as to transmit and receive ultrasonic waves to and from a subject (not shown), one or more (three layers are illustrated) acoustic matching layer 12 (12a, 12b and 12c) provided on a front surface (upper surface in FIG. 12) at a subject side of the piezoelectric elements 11, an acoustic lens 13 provided on a surface at the subject side of the acoustic matching layer 12, and a backing load member 14 provided on a rear surface of the piezoelectric elements 11 at a side opposite to the acoustic matching layer 12.
Unillustrated electrodes are disposed on the front surface and the rear surface of the piezoelectric elements 11, respectively so that electric signals can be transmitted and received to and from the piezoelectric elements 11. The piezoelectric elements 11 are formed of PZT-based piezoelectric ceramic materials, or single-crystal piezoelectric materials, a piezoelectric composite made of the materials and polymers, or piezoelectric polymers typified by PVDF or the like. The piezoelectric elements 11 are configured to convert a voltage into ultrasonic waves to be transmitted to the inside of the subject or to convert an echo signal reflected from the inside of the subject into an electric signal to be received thereto. In the illustrated example, the plurality of piezoelectric elements 11 is arranged in the X direction. Such an arrangement of the plurality of piezoelectric elements 11 allows electronically scanning ultrasonic waves to be deflected or converged, thereby enabling a so-called electronic scanning.
The acoustic matching layer 12 is provided in order to efficiently transmit and receive ultrasonic waves to and from the inside of the subject. More specifically, the acoustic matching layer 12 performs a function of gradually matching an acoustic impedance of the piezoelectric elements 11 to an acoustic impedance of the subject. In the illustrated example, although three acoustic matching layers 12a, 12b, and 12c are provided, the acoustic matching layers may have one, two, or four or more layers. Moreover, in the illustrated example, although the acoustic matching layer 12 is integrally formed on the plurality of piezoelectric elements 11, the acoustic matching layer 12 is divided so as to correspond to the respective piezoelectric elements 11. Furthermore, there is known a structure that can increase the directivity of ultrasonic waves (for example, see Patent Documents 1 and 2).
The acoustic lens 13 performs a function of condensing an ultrasonic beam in order to increase resolution of a diagnostic image. In the illustrated example, the acoustic lens 13 extends in the Y direction shown in the drawing (a direction orthogonal to the arrangement direction X of the piezoelectric elements 11) with a semi-circular shape that is convex in the Z direction, and is capable of narrowing the ultrasonic waves in the Y direction. The acoustic lens 13 is an optional element and thus will be provided as necessary.
The backing load member 14 performs a function of holding the piezoelectric elements 11 by being coupled to them and attenuating unnecessary ultrasonic waves. In the drawings of this specification, the X direction will be referred to as “the arrangement direction (of the piezoelectric elements),” the Y direction will be referred to as “the width direction (of the piezoelectric elements),” and the Z direction will be referred to as “the thickness direction (of the piezoelectric elements).”
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2003-125494
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2005-198261